Hydroelectric Power Generation - Renewable Energy: Technology, Economics and Environment - page 360

Intake. The intake establishes the connection between the headwater and the tur-
bine. At the entrance of the intake, there is normally a trash rack keeping floating
debris away from the plant. Gates or stoplogs are also integrated into the intake
structure in order to seal the hydroelectric power station during maintenance
works or to interrupt the flow into the power station in case of an accident. For
very small plants these security installations are not necessary or are installed as
simple sliding gates.
Headrace/Penstock. Water from the reservoir either flows directly through an
intake or initially via a headrace channel, tunnel or pipe, and a penstock to the
turbine. It is important to keep hydraulic losses at a minimum, which usually is
achieved by large enough cross-sections and hydraulically suitable cross-section
geometry.
If required, the so-called surge tank is located in front of the intake into the
penstock. It reduces water hammer and pressure fluctuations that occur when
starting and shutting the plant down, but also during each load alternation because
of the water's inherent inertia.
The hydraulic connection between the headwater or the intake structure, and
the turbine is established through the tunnel and the penstock and the distance be-
tween the plant components is overcome. Because of losses along the upstream
waterway (i.e. intake structure, tunnel, penstock) a small part of the water's poten-
tial energy cannot be used for energy production.
Depending on the topography, but also the ecological and economic framework
conditions, various combinations of upstream waterways are possible. As one ex-
ample, the inflow from the headwater can be realised via an open upstream chan-
nel or as a pressure-free low gradient tunnel. In run-of-river power stations with
low head, the water can flow directly from the intake structure to the turbine. In
that case the tunnel, surge tank and penstock are not required.
Penstocks are normally built from individual pipe segments of welded steel
pipes. Tunnels can be built for open channel flow, low-pressure or high-pressure
flow. Depending on the hydraulic requirements, they either have a reinforced con-
crete lining or, in particular with high-pressure plants, a steel armour. In small
power plants other materials are used for the upstream inflow (e.g. PVC pipes or
more recently, wooden pipes with straining rings).
Powerhouse. In the powerhouse the main parts of a hydroelectric power station
are situated. These are turbines, sometimes transmissions, generators, control sys-
tems, in some cases a transformer with an electric power substation and some-
times shut-off valves for the pipelines.
Turbines. The hydraulic machine that converts the upstream energy into a rota-
tion is called turbine. Water wheels were the forerunners, but they are only rarely
used nowadays.